In known combine harvesters, grain is threshed and separated in a threshing and separating mechanism and the separated grain, together with impurities of all sorts, such as chaff, dust, straw particles and tailings, is fed to a cleaning mechanism for cleaning. Clean grain is collected below the cleaning mechanism and fed to a grain tank for temporary storage. The tailings are separated from the clean grain and impurities for reprocessing. This reprocessing either involves recycling the tailings through the threshing and separating mechanism or treating them in a separate tailings rethreshing means. In both cases the tailings are conveyed through an elevator which usually is of the paddle type but which also may consist of any other suitable type of conveying means such as an ejector blower or an auger conveyor.
In conventional combine harvesters, wherein the tailings are recycled through the threshing and separating mechanism, a tailings elevator extends at one side of the machine between a location beneath the cleaning mechanism, where the tailings are collected, and a location forwardly and generally above the level of the threshing means at one side thereof and at which location the elevator supplies the tailings to a transverse tailings distributing auger which is operable to spread the tailings more or less evenly across the width of the threshing mechanism. This arrangement of the tailings elevator and the distributing auger is relatively long and hence is expensive and takes up much room, whereby it is cumbersome and access to other components of the machine and drive means therefor is hampered considerably.
Instead of using a tailings distributing auger, it is proposed in DE-A-2.037.446 to discharge the tailings from the tailings elevator by means of a paddle rotor which throws the tailings against a series of chain portions, dangling transversely in front of the threshing mechanism and intended to provide a spreading effect on the tailings flow. While efficient spreading is accomplished, such an arrangement is found to be very sensitive to the tailings flow rate, the composition of the tailings and the density thereof as a result of the uncontrolled rebounding of grain kernels against the chain portions.
In present large capacity machines, the threshing and separating devices have a considerable width, calling for high demands where distribution of the recycled tailings is concerned. Moreover, regardless of the kind of distributing device employed, small percentages of tailings on large capacity machines represent considerable volumes whereby the recycling of these volumes of tailings through the threshing and separating mechanism often may lead to uneven loading and/or overloading of the various components which ultimately results in considerable grain losses.
In other known combine harvesters, independent tailings rethreshers have been provided which are normally arranged to receive the tailings from the cleaning mechanism and to discharge the rethreshed tailings onto the grain pan of the cleaning mechanism to recycle the tailings therethrough. This arrangement is advantageous in as far as the main threshing and separating mechanism can be used to its full capacity without any risk of unevenly loading or overloading it with tailings.
Nevertheless, recycling the tailings directly through the cleaning mechanism also has some disadvantages, a major one arising from the fact that, due to the confined space between the threshing and separating mechanism on the one hand and the cleaning mechanism on the other hand, it is very difficult to provide adequate tailings distributing means which satisfactorily spread the tailings evenly over the cleaning mechanism without hampering the operation of the threshing and separating mechanism as well as the cleaning mechanism.
For this reason, most tailings return devices which recycle the tailings through the cleaning mechanism do not comprise specific distributing means but try to obtain some spreading effect by forcefully ejecting the tailings onto the rear end of the grainpan or eventually onto the front portion of the sieves of the cleaning mechanism from one or both transverse sides of the harvester. A combine harvester employing a tailings recycling mechanism of this nature is disclosed in GB-A-1.136.202. It should be appreciated however that the spreading pattern of the tailings is easily disturbed due to varying volumes or density changes of recycled tailings, which result from varying crop conditions, or varying harvesting conditions, such as operation on transversely inclined slopes.
Moreover, it is well known in the art that the reciprocating action of the cleaning mechanism in general and the grainpan in particular causes a preconditioning effect to the layer of crop material. The grain kernels contained in such layer are urged to sink therethrough and to concentrate at a bottom portion thereof in order to prepare the layer for subsequent cleaning action by the cleaning sieves. Accordingly, discharging the tailings on top of the transported layer at a location behind the threshing and separating area, i.e., already a considerable distance away from the front of the cleaning mechanism and thus at a location where a substantial degree of preconditioning already has occurred, completely undoes the preconditioned state of the layer.
Furthermore, a cleaning mechanism of a combine harvester normally is composed of separate lengthwise sections separated by upstanding dividers which are present on grainpans as well as on cleaning sieves and which are operable to allow only for restricted sideways movement of crop material transported by the cleaning mechanism. When discharging the tailings from a transverse side of the harvester under a sharp angle onto the top of the layer of crop material supported and transported by the grainpan, the grain kernels contained in said tailings have a tendency to penetrate said layer and to continue their trajectory until movement thereof is restricted by a divider, delimiting, in that direction, the section in which the grain kernels have been projected. As a result of this action, grain starts to accumulate on one side of a section whereas the chaff material of the transported layer, which is much lighter than the grain, is dispelled to the other transverse side of the section whereby the even distribution of grain and chaff transversely of a section becomes disturbed. It is clear that concentrating the grain on one side of a section and the chaff material at the other side thereof, results in overloading and underloading of the respective section sides, leading ultimately to grain losses at both sides of a section.